This invention relates to a coordinate reader for delivering coordinate information to a central device such as a computer, and more particularly to a coordinate reader of the electromagnetic induction type in which coordinate information is produced by electromagnetic induction.
Generally, a coordinate is obtained by successively scanning sense lines close to the current position of a coordinate pointer to detect induced signals induced in these sense lines and by subjecting such induced signals to comparison/calculation processing.
FIG. 2 shows the amplitude of several induced signals on a time base. VP is a maximum-amplitude main peak signal; thus, the coordinate pointer is laid in the vicinity of the sense line delivering the maximum-amplitude main peak signal. Generally, the spacing between adjacent sense lines is larger than the degree of resolution required for a coordinate value; therefore, a more accurate position of the coordinate pointer between adjacent sense lines is obtained by subjecting VP, and Vpl and Vph which are the signals on the sense lines preceding and subsequent to VP to comparison/calculation processing.
In the example of FIG. 2, Vph&gt;Vpl, and the coordinate pointer is displaced from the sense line having the induced voltage VP in the scanning direction (toward the sense line having the induced voltage Vph). The coordinate value is obtained with a given degree of resolution of, for example, 0.1 mm by processing the signals Vp, Vpl and Vph.